NOx treated mixed metal oxide catalyst

ABSTRACT

An improved catalyst comprising a mixed metal oxide, either promoted or not, is useful for the vapor phase oxidation of an alkane or a mixture of an alkane and an alkene to an unsaturated carboxylic acid and for the vapor phase ammoxidation of an alkane or a mixture of an alkane and an alkene to an unsaturated nitrile.

CROSS-REFERENCE TO RELATED APPLICATIONS

This non-provisional application is a divisional of non-provisional U.Spatent application Ser. No. 10/731,523 filed Dec. 9, 2003 now U.S. Pat.No. 6,943,145, benefit of which is claimed under 35 U.S.C. §120 andwhich is a continuation-in-part of non-provisional U.S. patentapplication Ser. No. 10/116,241 filed Apr. 4, 2002, now U.S. Pat. No.6,818,588, benefit of which is also claimed under 35 U.S.C. §120 andwhich in turn claims benefit under 35 U.S.C. §119(e) of U.S. provisionalApplication No, 60/283,260 filed Apr. 12, 2001, priority of which isclaimed for the present application.

The present invention relates to improved catalysts for the oxidation ofalkanes, or a mixture of alkanes and alkenes, to their correspondingunsaturated carboxylic acids of unsaturated nitriles by vapor phasecatalytic oxidation, as well as to a method of making the catalysts. Thepresent invention also relates to a method of producing unsaturatedcarboxylic acids by subjecting alkanes, or a mixture of alkanes andalkenes, to vapor phase catalytic oxidation in the presence of theimproved catalysts. The present invention also relates to a method ofproducing unsaturated nitriles by subjecting alkanes or a mixture ofalkanes and alkenes to vapor phase catalytic oxidation in the presenceof ammonia and the improved catalysts.

Unsaturated carboxylic acids such as acrylic acid and methacrylic acidare industrially important as starting materials for various syntheticresins, coating materials and plasticizers. Commercially, the currentprocess for acrylic acid manufacture involves a two-step catalyticoxidation reaction starting with a propene feed. In the first stage,propene is converted to acrolein over a modified bismuth molybdatecatalyst. In the second stage, acrolein product from the first stage isconverted to acrylic acid using a catalyst composed of mainly molybdenumand vanadium oxides. In most cases, the catalyst formulations areproprietary to the catalyst supplier, but, the technology is wellestablished. Moreover, there is an incentive to develop a single stepprocess to prepare the unsaturated acid from its corresponding alkene.Therefore, the prior art describes cases where complex metal oxidecatalysts are utilized for the preparation of unsaturated acid from acorresponding alkene in a single step.

European Published Patent Application No. 0 630 879 B1 discloses aprocess for producing an unsaturated aldehyde and a carboxylic acidwhich comprises subjecting propene, isobutene or tertiary butanol to gasphase catalytic oxidation with molecular oxygen in the presence of (i) acatalyst composite oxide represented by the formulaMo_(a)Bi_(b)Fe_(c)A_(d)B_(e)C_(f)D_(g)O_(x)wherein A represents Ni and/or Co, B represents at least one elementselected from Mn, Zn, Ca, Mg, Sn and Pb, C represents at least oneelement selected from P, B, As, Te, W, Sb and Si, and D represents atleast one element selected from K, Rb, Cs and Tl; andwherein, when a=12, 0<b≦10, 0<c≦10, 1≦d≦10, 0≦e≦10, 0≦f≦20 and 0≦g≦2,and x has a value dependent on the oxidation state of the otherelements; and (ii) a molybdenum oxide which in itself is substantiallyinert to said gas phase catalytic oxidation to provide the correspondingunsaturated aldehyde and unsaturated carboxylic acid.

Japanese Laid-Open Patent Application Publication No. 07-053448discloses the manufacture of acrylic acid by the gas-phase catalyticoxidation of propene in the presence of mixed metal oxides containingMo, V, Te, O and X wherein X is at least one of Nb, Ta, W, Ti, Al, Zr,Cr, Mn, Fe, Ru, Co, Rh, Ni, Pd, Pt, Sb, Bi, B, In, Li, Na, K, Rb, Cs andCe.

Published International Application No. WO 00/09260 discloses a catalystfor selective oxidation of propene to acrylic acid and acroleincontaining a catalyst composition comprising the elements Mo, V, La, Pd,Nb and X in the following ratio:Mo_(a)V_(b)La_(c)Pd_(d)Nb_(e)X_(f)

wherein X is Cu or Cr or a mixture thereof,

a is 1,

b is 0.01 to 0.9,

c is >0 to 0.2

d is 0.0000001 to 0.2,

e is 0 to 0.2, and

f is 0 to 0.2; and

wherein the numerical values of a, b, c, d, e and f represent therelative gram-atom ratios of the elements Mo, V, La, Pd, Nb and X,respectively, in the catalyst and the elements are present incombination with oxygen.

Commercial incentives also exist for producing acrylic acid using alower cost propane feed. Therefore, the prior art describes caseswherein a mixed metal oxide catalyst is used to convert propane toacrylic acid in one step.

U.S. Pat. No. 5,380,933 discloses a method for producing an unsaturatedcarboxylic acid comprising subjecting an alkane to a vapor phasecatalytic oxidation reaction in the presence of a catalyst containing amixed metal oxide comprising, as essential components, Mo, V, Te, O andX, wherein X is at least one element selected from the group consistingof niobium, tantalum, tungsten, titanium, aluminum, zirconium, chromium,manganese, iron, ruthenium, cobalt, rhodium, nickel, palladium,platinum, antimony, bismuth, boron, indium and cerium; and wherein theproportions of the respective essential components, based on the totalamount of the essential components, exclusive of oxygen, satisfy thefollowing relationships:

0.25<r(Mo)<0.98, 0.003<r(V)<0.5, 0.003<r(Te)<0.5 and 0.003<r(X)<0.5,wherein r(Mo), r(V), r(Te) and r(X) are the molar fractions of Mo, V, Teand X, respectively, based on the total amount of the essentialcomponents exclusive of oxygen.

Published International Application No. WO 00/29106 discloses a catalystfor selective oxidation of propane to oxygenated products includingacrylic acid, acrolein and acetic acid, said catalyst system containinga catalyst composition comprisingMo_(a)V_(b)Ga_(c)Pd_(d)Nb_(e)X_(f)

wherein X is at least one element selected from La, Te, Ge, Zn, Si, Inand W,

a is 1,

b is 0.01 to 0.9,

c is >0 to 0.2,

d is 0.0000001 to 0.2,

e is >0 to 0.2, and

f is 0.0 to 0.5; and

wherein the numerical values of a, b, c, d, e and f represent therelative gram-atom ratios of the elements Mo, V, Ga, Pd, Nb and X,respectively, in the catalyst and the elements are present incombination with oxygen.

Japanese Laid-Open Patent Application Publication No. 2000-037623discloses a method for producing an unsaturated carboxylic acidcomprising subjecting an alkane to a vapor phase catalytic oxidation inthe presence of a catalyst having the empirical formulaMoV_(a)Nb_(b)X_(c)Z_(d)O_(n)wherein X is at least one element selected from the group consisting ofTe and Sb, Z is at least one element selected from the group consistingof W, Cr, Ta, Ti, Zr, Hf, Mn, Re, Fe, Ru, Co, Rh, Ni, Pd, Pt, Ag, Zn, B,Al, Ga, In, Ge, Sn, Pb, P, Bi, Y, rare earth elements and alkaline earthelements, 0.1≦a≦1.0, 0.01≦b≦1.0, 0.01≦c≦1.0, 0≦d≦1.0 and n is determinedby the oxidation states of the other elements.

Nitriles, such as acrylonitrile and methacrylonitrile, have beenindustrially produced as important intermediates for the preparation offibers, synthetic resins, synthetic rubbers, and the like. The mostpopular method for producing such nitriles is to subject an olefin suchas propene or isobutene to a catalytic reaction with ammonia and oxygenin the presence of a catalyst in a gaseous phase at a high temperature.Known catalysts for conducting this reaction include a Mo—Bi—P—Ocatalyst, a V—Sb—O catalyst, a Sb—U—V—Ni—O catalyst, a Sb—Sn—O catalyst,a V—Sb—W—P—O catalyst and a catalyst obtained by mechanically mixing aV—Sb—W—O oxide and a Bi—Ce—Mo—W—O oxide. However, in view of the pricedifference between propane and propene or between isobutane andisobutene, attention has been drawn to the development of a method forproducing acrylonitrile or methacrylonitrile by an ammoxidation reactionwherein a lower alkane, such as propane or isobutane, is used as astarting material, and it is catalytically reacted with ammonia andoxygen in a gaseous phase in the presence of a catalyst.

In particular, U.S. Pat. No. 5,281,745 discloses a method for producingan unsaturated nitrile comprising subjecting an alkane and ammonia inthe gaseous state to catalytic oxidation in the presence of a catalystwhich satisfies the conditions:

(1) the mixed metal oxide catalyst is represented by the empiricalformulaMo_(a)V_(b)Te_(c)X_(x)O_(n)wherein X is at least one element selected from the group consisting ofniobium, tantalum, tungsten, titanium, aluminum, zirconium, chromium,manganese, iron, ruthenium, cobalt, rhodium, nickel, palladium,platinum, antimony, bismuth, boron and cerium and, when a=1, b=0.01 to1.0, c=0.01 to 1.0, x=0.01 to 1.0 and n is a number such that the totalvalency of the metal elements is satisfied; and

(2) the catalyst has X-ray diffraction peaks at the following angles(±0.3°) of 2θ in its X-ray diffraction pattern: 22.1°, 28.2°, 36.2°,45.2° and 50.0°.

Similarly, Japanese Laid-Open Patent Application Publication No.6-228073 discloses a method of nitrile preparation comprising reactingan alkane in a gas phase contact reaction with ammonia in the presenceof a mixed metal oxide catalyst of the formulaW_(a)V_(b)Te_(c)X_(x)O_(n)wherein X represents one or more elements selected from niobium,tantalum, titanium, aluminum, zirconium, chromium, manganese, iron,ruthenium, cobalt, rhodium, nickel, palladium, platinum, antimony,bismuth, indium and cerium and, when a=1, b=0.01 to 1.0, c=0.01 to 1.0,x=0.01 to 1.0 and n is determined by the oxide form of the elements.

U.S. Pat. No. 6,043,185 also discloses a catalyst useful in themanufacture of acrylonitrile or methacrylonitrile by the catalyticreaction in the vapor phase of a paraffin selected from propane andisobutane with molecular oxygen and ammonia by catalytic contact of thereactants in a reaction zone with a catalyst, wherein the catalyst hasthe empirical formulaMo_(a)V_(b)Sb_(c)Ga_(d)X_(e)O_(x)where X is one or more of As, Te, Se, Nb, Ta, W, Ti, Zr, Cr, Mn, Fe, Ru,Co, Rh, Ni, Pd, Pt, B, In, Ce, Re, Ir, Ge, Sn, Bi, Y, Pr, an alkalimetal and an alkaline earth metal; and when a=1, b=0.0 to 0.99, c=0.01to 0.9, d=0.01 to 0.5, e=0.0 to 1.0 and x is determined by the oxidationstate of the cations present.

Despite the above-noted attempts to provide new and improved catalystsfor the oxidation of alkanes to unsaturated carboxylic acids and for theammoxidation of alkanes to unsaturated nitrites, one impediment to theprovision of a commercially viable process for such catalytic oxidationsis the identification of a catalyst providing adequate conversion andsuitable selectivity, thereby providing sufficient yield of theunsaturated product.

By the present invention, there are provided catalysts wherein theperformance is enhanced by treating mixed metal oxide catalystprecursors with a source of NO_(x) to form a treated admixture, andcalcining the treated admixture while the NO_(x) is present in theadmixture. The performance of various types of catalysts may be enhancedby treating mixed metal oxide catalyst precursors, including, but notlimited to, mixed metal oxide catalysts and promoted mixed metal oxidecatalysts, with a source of NO_(x).

Thus, in a first aspect, the present invention provides a process forimproving the performance characteristics of a catalyst, comprising thesteps of:

a) providing precursors for a promoted mixed metal oxide having theempirical formulaJ_(j)M_(m)N_(n)Y_(y)Z_(z)O_(o)wherein J is at least one element selected from the group consisting ofMo and W, M is at least one element selected from the group consistingof V and Ce, N is at least one element selected from the groupconsisting of Te, Sb and Se, Y is at least one element selected from thegroup consisting of Nb, Ta, Ti, Al, Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pt,Sb, Bi, B, In, As, Ge, Sn, Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba,Ra, Hf, Pb, P, Pm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu, and Z is selectedfrom the group consisting of Ni, Pd, Cu, Ag and Au; and wherein, whenj=1, m=0.01 to 1.0, n=0.01 to 1.0, y=0.01 to 1.0, z=0.001 to 0.1 and ois dependent on the oxidation state of the other elements;

b) adding a source of NO_(x) to said precursors to form an admixture;and

c) calcining said admixture while said NO_(x) is present in saidadmixture.

In a second aspect, the present invention provides a process forproducing an unsaturated carboxylic acid, which comprises subjecting analkane or a mixture of an alkane and an alkene to a vapor phasecatalytic oxidation reaction in the presence of a promoted catalystcontaining a mixed metal oxide having the empirical formulaJ_(j)M_(m)N_(n)Y_(y)Z_(z)O_(o)wherein J is at least one element selected from the group consisting ofMo and W, M is at least one element selected from the group consistingof V and Ce, N is at least one element selected from the groupconsisting of Te, Sb and Se, Y is at least one element selected from thegroup consisting of Nb, Ta, Ti, Al, Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pt,Sb, Bi, B, In, As, Ge, Sn, Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr. Ba,Ra, Hf, Pb, P, Pm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu, and Z is selectedfrom the group consisting of Ni, Pd, Cu, Ag and Au; and wherein, whenj=1, m=0.01 to 1.0, n=0.01 to 1.0, y=0.01 to 1.0, z=0.001 to 0.1 and ois dependent on the oxidation state of the other elements. The catalystcomposition, while in its precursor state, is treated with an NO_(x)source, such as nitric acid, and calcined.

In a third aspect, the present invention provides a process forproducing an unsaturated nitrile, which comprises subjecting an alkane,or a mixture of an alkane and an alkene, and ammonia to a vapor phasecatalytic oxidation reaction in the presence of a promoted catalystcontaining a mixed metal oxide having the empirical formulaJ_(j)M_(m)N_(n)Y_(y)Z_(z)O_(o)wherein J is at least one element selected from the group consisting ofMo and W, M is at least one element selected from the group consistingof V and Ce, N is at least one element selected from the groupconsisting of Te, Sb and Se, Y is at least one element selected from thegroup consisting of Nb, Ta, Ti, Al, Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pt,Sb, Bi, B, In, As, Ge, Sn, Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba,Ra, Hf, Pb, P, Pm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu, and Z is selectedfrom the group consisting of Ni, Pd, Cu, Ag and Au; and wherein, whenj=1, m=0.01 to 1.0, n=0.01 to 1.0, y=0.01 to 1.0, z=0.001 to 0.1 and ois dependent on the oxidation state of the other elements. The catalystcomposition, while in its precursor state, is treated with an NO_(x)source, such as nitric acid, and calcined.

In a fourth aspect of the present invention, a promoted catalystcomposition is provided containing a mixed metal oxide having theempirical formulaJ_(j)M_(m)N_(n)Y_(y)Z_(z)O_(o)wherein J is at least one element selected from the group consisting ofMo and W, M is at least one element selected from the group consistingof V and Ce, N is at least one element selected from the groupconsisting of Te, Sb and Se, Y is at least one element selected from thegroup consisting of Nb, Ta, Ti, Al, Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pt,Sb, Bi, B, In, As, Ge, Sn, Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba,Ra, Hf, Pb, P, Pm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu, and Z is selectedfrom the group consisting of Ni, Pd, Cu, Ag and Au; and wherein, whenj=1, m=0.01 to 1.0, n=0.01 to 1.0, y=0.01 to 1.0, z=0.001 to 0.1 and ois dependent on the oxidation state of the other elements. The catalystcomposition is treated to exhibit peaks at X-ray diffraction angles (2θ)of 22.1°, 27.1°, 28.2°, 36.2°, 45.2°, and 50.0°, with a relativeincrease in a diffraction peak at the diffraction angle (2θ) of 27.1degrees when compared with an untreated catalyst of like empiricalformula.

In this regard, in addition to the above noted peak at 27.1 degrees, thepreferred mixed metal oxide exhibits the following five main diffractionpeaks at specific diffraction angles (2θ) in the X-ray diffractionpattern of the treated mixed metal oxide (as measured using Cu-Kαradiation as the source):

X-ray lattice plane Diffraction angle 2θ Spacing medium Relative (±0.3°)(Å) Intensity 22.1° 4.02 100 28.2° 3.16 20~150 36.2° 2.48 5~60 45.2°2.00 2~40 50.0° 1.82 2~40

The intensity of the X-ray diffraction peaks may vary upon the measuringof each crystal. However, the intensity, relative to the peak intensityat 22.1° being 100, is usually within the above-ranges. Generally, thepeak intensities at 2θ=22.1° and 28.2° are distinctly observed. However,so long as the above five diffraction peaks are observable, the basiccrystal structure is the same even if other peaks are observed inaddition to the five diffraction peaks (e.g. at 27.1 degrees), and sucha structure is useful for the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the performance of the catalysts of the ComparativeExamples and the Examples of the present invention, in terms ofconversion and selectivity, when used to produce acrylic acid frompropane.

Turning now in more specific detail to the first aspect of the presentinvention, the mixed metal oxide is prepared by treating a catalystprecursor admixture with a source of NO_(x). It will be appreciated thatthe reference to NO_(x) herein is intended to cover compounds includingnitrogen and oxygen, without limitation as to the specificstoichiometric amounts. However, in a preferred embodiment, x ranges upto 3, and more preferably is an integer selected from 1 or 2.

In a first step, a catalyst precursor admixture may be formed byadmixing metal compounds, preferably at least one of which containsoxygen, and at least one solvent, in appropriate amounts to form theadmixture, which may be a slurry, solution or combination thereof. Asource of NO_(x) is provided and contacted with at least a portion ofthe precursor admixture. Liquids are then removed, and the precursoradmixture calcined. More specifically, as mentioned, though a slurry maybe formed, preferably, a precursor solution is instead formed at thisstage of the catalyst preparation.

Where it is desired to make an improved mixed metal oxide catalyst,generally, the metal compounds in the solution will contain elements A,D, E, X and O, such that a mixed metal oxide catalyst precursor will beformed having the empirical formula:A_(a)D_(b)E_(c)X_(d)O_(e)wherein A is at least one element selected from the group consisting ofMo and W, D is at least one element selected from the group consistingof V and Ce, E is at least one element selected from the groupconsisting of Te, Sb and Se, and X is at least one element selected fromthe group consisting of Nb, Ta, Ti, Al, Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni,Pt, Sb, Bi, B, In, As, Ge, Sn, Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr,Ba, Hf, Pb, P, Pm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu; and a=1, b=0.01 to1.0, c=0.01 to 1.0, d=0.01 to 1.0, and e is dependent on the oxidationstate of the other elements

Where it is desired to make an improved promoted mixed metal oxidecatalyst, generally, the metal compounds in the solution will containelements J, M, N, Y, Z and O, such that a promoted mixed metal oxidecatalyst precursor will be formed, as previously defined, i.e., havingthe empirical formula:J_(j)M_(m)N_(n)Y_(y)Z_(z)O_(o)wherein J is at least one element selected from the group consisting ofMo and W, M is at least one element selected from the group consistingof V and Ce, N is at least one element selected from the groupconsisting of Te, Sb and Se, Y is at least one element selected from thegroup consisting of Nb, Ta, Ti, Al, Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pt,Sb, Bi, B, In, As, Ge, Sn, Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba,Ra, Hf, Pb, P, Pm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu, and Z is selectedfrom the group consisting of Ni, Pd, Cu, Ag and Au; and wherein, whenj=1, m=0.01 to 1.0, n=0.01 to 1.0, y=0.01 to 1.0, z=0.001 to 0.1 and ois dependent on the oxidation state of the other elements.

It is noted that promoted mixed metal oxides having the empiricalformulae Mo_(j)V_(m)Te_(n)Nb_(y)Z_(z)O_(o) orW_(j)V_(m)Te_(n)Nb_(y)Z_(z)O_(o), wherein Z, j, m, n, y, z and o are aspreviously defined, are particularly suitable for use in connection withthe present invention. Additional suitable embodiments are either of theaforesaid empirical formulae, wherein Z is Pd. Suitable solvents for theprecursor solution include water; alcohols including , but not limitedto, methanol, ethanol, propanol, and diols, etc.; as well as other polarsolvents known in the art. Generally, water is preferred. The water isany water suitable for use in chemical syntheses including, withoutlimitation, distilled water and de-ionized water. The amount of waterpresent is preferably an amount sufficient to keep the elementssubstantially in solution long enough to avoid or minimize compositionaland/or phase segregation during the preparation steps. Accordingly, theamount of water will vary according to the amounts and solubilities ofthe materials combined. Preferably, though lower concentrations of waterare possible for forming a slurry, as stated above, the amount of wateris sufficient to ensure an aqueous solution is formed, at the time ofmixing.

The precursor admixture is treated with a source of NO_(x). In apreferred embodiment, the treatment is performed by further admixing theprecursor admixture with a fluid for introducing NO_(x) to the precursoradmixture and then drying or calcining the resulting admixture.Accordingly, preferably the fluid includes a NO_(x) source such asnitric acid, ammonium nitrate, ammonium nitrite, NO, NO₂ or a mixturethereof. More preferably, the fluid is a liquid, such as an aqueoussolution, including the NO_(x) source dissolved or dispersed therein. Inanother embodiment, it is contemplated that a gas including a source ofNO_(x) is bubbled or otherwise introduced into the precursor admixturefor treating the admixture. In a highly preferred embodiment, theprecursor admixture prior to calcination is prepared by mixing theprecursor admixture and nitric acid solution to form a resultingadmixture having 0.01 to 20 percent by weight of nitric acid, and morepreferably 0.05 to 10 percent by weight of nitric acid. In yet anotherpreferred embodiment, the resulting admixture has 0.1 to 1.5 percent byweight of nitric acid. Alternatively expressed, prior to calcination,preferably the nitric acid is present in an amount of at least 500 ppmof the admixture, more preferably, at least 1500 ppm. An example of apreferred range of concentrations includes 1000 to 15,000 ppm nitricacid.

In another embodiment, where the source of NO_(x) includes NO₂, theamount of NO₂ ranges from 500 to 12,000 ppm and more preferably 1000 to9000 ppm.

By way of example, when a mixed metal oxide of the formulaMo_(a)V_(b)Te_(c)Nb_(d)O_(e) (wherein the element A is Mo, the element Dis V, the element E is Te and the element X is Nb) is to be prepared, anaqueous solution of niobium oxalate and a solution of aqueous nitricacid may be added to an aqueous solution or slurry of ammoniumheptamolybdate, ammonium metavanadate and telluric acid, so that theatomic ratio of the respective metal elements would be in the prescribedproportions. In one specific illustration, it is further contemplatedthat a 5% aqueous nitric acid is mixed with niobium oxalate solution ina ratio of 1:10 to 1.25:1 parts by volume acid solution to oxalatesolution, and more preferably 1:5 to 1:1 parts by volume acid solutionto oxalate solution.

For example, when a promoted mixed metal oxide of the formulaMo_(j)V_(m)Te_(n)Nb_(y)Au_(z)O_(f) wherein the element J is Mo, theelement M is V, the element N is Te, the element Y is Nb, and theelement Z is Au, is to be prepared, an aqueous solution of niobiumoxalate may be added to an aqueous solution or slurry of ammoniumheptamolybdate, ammonium nietavanadate, telluric acid and ammoniumtetrachloroaurate, so that the atomic ratio of the respective metalelements would be in the prescribed proportions.

Once the resulting NO_(x) treated admixture is formed, the liquidtherein is removed by any suitable method, known in the art, for forminga catalyst precursor. Such methods include, without limitation, vacuumdrying, freeze drying, spray drying, rotary evaporation and air-drying.Vacuum drying is generally performed at pressures ranging from 10 mm Hgto 500 mm Hg. Freeze drying typically entails freezing the slurry orsolution, using, for instance, liquid nitrogen, and drying the frozenslurry or solution under vacuum. Spray drying is generally performedunder an inert atmosphere such as nitrogen or argon, with an inlettemperature ranging from 125° C. to 200° C. and an outlet temperatureranging from 75° C. to 150° C. Rotary evaporation is generally performedat a bath temperature of from 25° C. to 90° C. and at a pressure of from10 mm Hg to 760 mm Hg, preferably at a bath temperature of from 40° to90° C. and at a pressure of from 10 mm Hg to 350 mm Hg, more preferablyat a bath temperature of from 40° C. to 60° C. and at a pressure of from10 mm Hg to 40 mm Hg. Air drying may be effected at temperatures rangingfrom 25° C. to 90° C. Rotary evaporation or air-drying are generallypreferred.

Once obtained, the resulting catalyst precursor is calcined. Thecalcination may be conducted in an oxygen-containing atmosphere or inthe substantial absence of oxygen, e.g., in an inert atmosphere or invacuo. The inert atmosphere may be any material which is substantiallyinert, i.e., does not react or interact with, the catalyst precursor.Suitable examples include, without limitation, nitrogen, argon, xenon,helium or mixtures thereof. Preferably, the inert atmosphere is argon ornitrogen. The inert atmosphere may flow over the surface of the catalystprecursor or may not flow thereover (a static environment). When theinert atmosphere does flow over the surface of the catalyst precursor,the flow rate can vary over a wide range, e.g., at a space velocity offrom 1 to 500 hr⁻¹.

The calcination is usually performed at a temperature of from 350° C. to850° C., preferably from 400° C. to 700° C., more preferably from 500°C. to 640° C. The calcination is performed for an amount of timesuitable to form the aforementioned catalyst. Typically, the calcinationis performed for from 0.5 to 30 hours, preferably from 1 to 25 hours,more preferably for from 1 to 15 hours, to obtain the desired promotedmixed metal oxide.

In a preferred mode of operation, the catalyst precursor is calcined intwo stages. In the first stage, the catalyst precursor is calcined in anoxidizing environment (e.g. air) at a temperature of from 200° C. to400° C., preferably from 275° C. to 325° C. for from 15 minutes to 8hours, preferably for from 1 to 3 hours. In the second stage, thematerial from the first stage is calcined in a non-oxidizing environment(e.g., an inert atmosphere) at a temperature of from 500° C. to 700° C.,preferably for from 550° C. to 650° C., for 15 minutes to 8 hours,preferably for from 1 to 3 hours. Optionally, a reducing gas, such as,for example, ammonia or hydrogen, may be added during the second stagecalcination.

In a particularly preferred mode of operation, the catalyst precursor inthe first stage is placed in the desired oxidizing atmosphere at roomtemperature and then raised to the first stage calcination temperatureand held there for the desired first stage calcination time. Theatmosphere is then replaced with the desired non-oxidizing atmospherefor the second stage calcination, the temperature is raised to thedesired second stage calcination temperature and held there for thedesired second stage calcination time.

Although any type of heating mechanism, e.g., a furnace, may be utilizedduring the calcination, it is preferred to conduct the calcination undera flow of the designated gaseous environment. Therefore, it isadvantageous to conduct the calcination in a bed with continuous flow ofthe desired gas(es) through the bed of solid catalyst precursorparticles.

With calcination of the mixed metal oxide precursor formulation, acatalyst is formed having the formula A_(a)D_(b)E_(c)X_(d)O_(e), whereinA, D, E, X, O, a, b, c, d and e are as previously defined.

Similarly, with calcination of the promoted mixed metal oxide precursorformulation, a promoted catalyst is formed having the formulaJ_(j)M_(m)N_(n)Y_(y)Z_(z)O_(o), wherein J, M, N, Y, Z, O, j, m, n, y, zand o are as previously defined.

The starting materials for the above promoted mixed metal oxide are notlimited to those described above. A wide range of materials including,for example, oxides, nitrates, halides or oxyhalides, alkoxides,acetylacetonates, and organometallic compounds may be used. For example,ammonium heptamolybdate may be utilized for the source of molybdenum inthe catalyst. However, compounds such as MoO₃, MoO₂, MoCl₅, MoOCl₄,Mo(OC₂H₅)₅, molybdenum acetylacetonate, phosphomolybdic acid andsilicomolybdic acid may also be utilized instead of ammoniumheptamolybdate. Similarly, ammonium metavanadate may be utilized for thesource of vanadium in the catalyst. However, compounds such as V₂O₅,V₂O₃, VOCl₃, VCl₄, VO(OC₂H₅)₃, vanadium acetylaceton and vanadylacetylacetonate may also be utilized instead of ammonium metavanadate.The tellurium source may include telluric acid, TeCl₄, Te(OC₂H₅)₅,Te(OCH(CH₃)₂)₄ and TeO₂. The niobium source may include ammonium niobiumoxalate, Nb₂O₅, NbCl₅, niobic acid or Nb(OC₂H₅)₅ as well as the moreconventional niobium oxalate.

In addition, with reference to the promoter elements for the promotedcatalyst, the nickel source may include nickel(II) acetate tetrahydrate,Ni(NO₃)₂, nickel(II) oxalate, NiO, Ni(OH)₂, NiCl₂, NiBr₂, nickel(II)acetylacetonate, nickel(II) sulfate, NiS or nickel metal. The palladiumsource may include Pd(NO₃)₂, palladium(II) acetate, palladium oxalate,PdO, Pd(OH)₂, PdCl₂, palladium acetylacetonate or palladium metal. Thecopper source may be copper acetate, copper acetate monohydrate, copperacetate hydrate, copper acetylacetonate, copper bromide, coppercarbonate, copper chloride, copper chloride dihydrate, copper fluoride,copper formate hydrate, copper gluconate, copper hydroxide, copperiodide, copper methoxide, copper nitrate, copper nitrate hydrate, copperoxide, copper tartrate hydrate or a solution of copper in an aqueousinorganic acid, e.g., nitric acid. The silver source may be silveracetate, silver acetylacetonate, silver benzoate, silver bromide, silvercarbonate, silver chloride, silver citrate hydrate, silver fluoride,silver iodide, silver lactate, silver nitrate, silver nitrite, silveroxide, silver phosphate or a solution of silver in an aqueous inorganicacid, e.g., nitric acid. The gold source may be ammoniumtetrachloroaurate, gold bromide, gold chloride, gold cyanide, goldhydroxide, gold iodide, gold oxide, gold trichloride acid and goldsulfide.

As discussed previously, without limitation, examples of preferredNO_(x) sources include nitric acid, ammonium nitrate, ammonium nitrite,NO, NO₂ or a mixture thereof.

A mixed metal oxide (promoted or not), thus obtained, exhibits excellentcatalytic activities by itself. However, the mixed metal oxide can beconverted to a catalyst having higher activities by grinding. There isno particular restriction as to the grinding method, and conventionalmethods may be employed. As a dry grinding method, a method of using agas stream grinder may, for example, be mentioned wherein coarseparticles are permitted to collide with one another in a high speed gasstream for grinding. The grinding may be conducted not only mechanicallybut also by using a mortar or the like in the case of a small scaleoperation.

As a wet grinding method wherein grinding is conducted in a wet state byadding water or an organic solvent to the above mixed metal oxide, aconventional method of using a rotary cylinder-type medium mill or amedium-stirring type mill, may be mentioned. The rotary cylinder-typemedium mill is a wet mill of the type wherein a container for the objectto be ground is rotated, and it includes, for example, a ball mill and arod mill. The medium-stirring type mill is a wet mill of the typewherein the object to be ground, contained in a container is stirred bya stirring apparatus, and it includes, for example, a rotary screw typemill, and a rotary disc type mill.

The conditions for grinding may suitably be set to meet the nature ofthe above-mentioned promoted mixed metal oxide, the viscosity, theconcentration, etc. of the solvent used in the case of wet grinding, orthe optimum conditions of the grinding apparatus. However, it ispreferred that grinding is conducted until the average particle size ofthe ground catalyst precursor would usually be at most 20 μm, morepreferably at most 5 μm. Improvement in the catalytic performance mayoccur due to such grinding.

Further, in some cases, it is possible to further improve the catalyticactivities by further adding a solvent to the ground catalyst precursorto form a solution or slurry, followed by drying again. There is noparticular restriction as to the concentration of the solution orslurry, and it is usual to adjust the solution or slurry so that thetotal amount of the starting material compounds for the ground catalystprecursor is from 10 to 60 wt %. Then, this solution or slurry is driedby a method such as spray drying, freeze drying, evaporation to drynessor vacuum drying, preferably by the spray drying method. Further,similar drying may be conducted also in the case where wet grinding isconducted.

The mixed metal oxide (promoted or not) obtained by the above-mentionedmethod may be used as a final catalyst, but it may further be subjectedto heat treatment usually at a temperature of from 200° to 700° C. forfrom 0.1 to 10 hours.

The resulting mixed metal oxide (promoted or not) may be used by itselfas a solid catalyst. It also may be formed into a catalyst with asuitable carrier, such as, without limitation, silica, alumina, titania,aluminosilicate, diatomaceous earth or zirconia, according toart-disclosed techniques. Further, it may be processed to a suitableshape or particle size using art disclosed techniques, depending uponthe scale or system of the reactor.

Alternatively, the metal components of the presently contemplatedcatalyst may be supported on materials such as alumina, silica,silica-alumina, zirconia, titania, etc. by conventional incipientwetness techniques. In one typical method, solutions containing themetals are contacted with the dry support such that the support iswetted; then, the resultant wetted material is dried, for example, at atemperature from room temperature to 200° C. followed by calcination asdescribed above. In another method, metal solutions are contacted withthe support, typically in volume ratios of greater than 3:1 (metalsolution:support), and the solution agitated such that the metal ionsare ion-exchanged onto the support. The metal-containing support is thendried and calcined as detailed above.

Turning now in more specific detail to the second aspect of the presentinvention, the present invention provides a process for producing anunsaturated carboxylic acid, which comprises subjecting an alkane, or amixture of an alkane and an alkene (“alkane/alkene”), to a vapor phasecatalytic oxidation reaction in the presence of a catalyst containingthe above promoted mixed metal oxide, to produce an unsaturatedcarboxylic acid.

In the production of such an unsaturated carboxylic acid, it ispreferred to employ a starting material gas that contains steam. In sucha case, as a starting material gas to be supplied to the reactionsystem, a gas mixture comprising a steam-containing alkane, or asteam-containing mixture of alkane and alkene, and an oxygen-containinggas, is usually used. However, the steam-containing alkane, or thesteam-containing mixture of alkane and alkene, and the oxygen-containinggas may be alternately supplied to the reaction system. The steam to beemployed may be present in the form of steam gas in the reaction system,and the manner of its introduction is not particularly limited.

Further, as a diluting gas, an inert gas such as nitrogen, argon orhelium may be supplied. The molar ratio (alkane or mixture of alkane andalkene):(oxygen):(diluting gas):(H₂O) in the starting material gas ispreferably (1):(0.1 to 10):(0 to 20):(0.2 to 70), more preferably (1):(1to 5.0):(0 to 10):(5 to 40).

When steam is supplied together with the alkane, or the mixture ofalkane and alkene, as starting material gas, the selectivity for anunsaturated carboxylic acid is distinctly improved, and the unsaturatedcarboxylic acid can be obtained from the alkane, or mixture of alkaneand alkene, in good yield simply by contacting in one stage. However,the conventional technique utilizes a diluting gas such as nitrogen,argon or helium for the purpose of diluting the starting material. Assuch a diluting gas, to adjust the space velocity, the oxygen partialpressure and the steam partial pressure, an inert gas such as nitrogen,argon or helium may be used together with the steam.

As the starting material alkane it is preferred to employ a C₃₋₈ alkane,particularly propane, isobutane or n-butane; more preferably, propane orisobutane; most preferably, propane. According to the present invention,from such an alkane, an unsaturated carboxylic acid such as anα,β-unsaturated carboxylic acid can be obtained in good yield. Forexample, when propane or isobutane is used as the starting materialalkane, acrylic acid or methacrylic acid will be obtained, respectively,in good yield.

In the present invention, as the starting material mixture of alkane andalkene, it is preferred to employ a mixture of C₃₋₈ alkane and C₃₋₈alkene, particularly propane and propene, isobutane and isobutene orn-butane and n-butene. As the starting material mixture of alkane andalkene, propane and propene or isobutane and isobutene are morepreferred. Most preferred is a mixture of propane and propene. Accordingto the present invention, from such a mixture of an alkane and analkene, an unsaturated carboxylic acid such as an α,β-unsaturatedcarboxylic acid can be obtained in good yield. For example, when propaneand propene or isobutane and isobutene are used as the starting materialmixture of alkane and alkene, acrylic acid or methacrylic acid will beobtained, respectively, in good yield. Preferably, in the mixture ofalkane and alkene, the alkene is present in an amount of at least 0.5%by weight, more preferably at least 1.0% by weight to 95% by weight;most preferably, 3% by weight to 90% by weight.

As an alternative, an alkanol, such as isobutanol, which will dehydrateunder the reaction conditions to form its corresponding alkene, i.e.isobutene, may also be used as a feed to the present process or inconjunction with the previously mentioned feed streams.

The purity of the starting material alkane is not particularly limited,and an alkane containing a lower alkane such as methane or ethane, airor carbon dioxide, as impurities, may be used without any particularproblem. Further, the starting material atkane may be a mixture ofvarious alkanes. Similarly, the purity of the starting material mixtureof alkane and alkene is not particularly limited, and a mixture ofalkane and alkene containing a lower alkene such as ethene, a loweralkane such as methane or ethane, air or carbon dioxide, as impurities,may be used without any particular problem. Further, the startingmaterial mixture of alkane and alkene may be a mixture of variousalkanes and alkenes.

There is no limitation on the source of the alkene. It may be purchased,per se, or in admixture with an alkane and/or other impurities.Alternatively, it can be obtained as a by-product of alkane oxidation.Similarly, there is no limitation on the source of the alkane. It may bepurchased, per se, or in admixture with an alkene and/or otherimpurities. Moreover, the alkane, regardless of source, and the alkene,regardless of source, may be blended as desired.

The detailed mechanism of the oxidation reaction of the presentinvention is not clearly understood, but the oxidation reaction iscarried out by oxygen atoms present in the above mixed metal oxide or bymolecular oxygen present in the feed gas. To incorporate molecularoxygen into the feed gas, such molecular oxygen may be pure oxygen gas.However, it is usually more economical to use an oxygen-containing gassuch as air, since purity is not particularly required.

It is also possible to use only an alkane, or a mixture of alkane andalkene, substantially in the absence of molecular oxygen for the vaporphase catalytic reaction. In such a case, it is preferred to adopt amethod wherein a part of the catalyst is appropriately withdrawn fromthe reaction zone from time to time, then sent to an oxidationregenerator, regenerated and then returned to the reaction zone forreuse. As the regeneration method of the catalyst, a method may, forexample, be mentioned which comprises contacting an oxidative gas suchas oxygen, air or nitrogen monoxide with the catalyst in the regeneratorusually at a temperature of from 300° to 600° C.

The second aspect of the present invention will be described in stillfurther detail with respect to a case where propane is used as thestarting material alkane and air is used as the oxygen source. Thereaction system may be preferably a fixed bed system. The proportion ofair to be supplied to the reaction system is important for theselectivity for the resulting acrylic acid, and it is usually at most 25moles, preferably from 0.2 to 18 moles per mole of propane, whereby highselectivity for acrylic acid can be obtained. This reaction can beconducted usually under atmospheric pressure, but may be conducted undera slightly elevated pressure or slightly reduced pressure. With respectto other alkanes such as isobutane, or to mixtures of alkanes andalkenes such as propane and propene, the composition of the feed gas maybe selected in accordance with the conditions for propane.

Typical reaction conditions for the oxidation of propane or isobutane toacrylic acid or methacrylic acid may be utilized in the practice of thepresent invention. The process may be practiced in a single pass mode(only fresh feed is fed to the reactor) or in a recycle mode (at least aportion of the reactor effluent is returned to the reactor). Generalconditions for the process of the present invention are as follows: thereaction temperature can vary from 200° C. to 700° C., but is usually inthe range of from 200° C. to 550° C., more preferably 250° C. to 480°C., most preferably 300° C. to 400° C.; the gas space velocity, SV, inthe vapor phase reaction is usually within a range of from 100 to 10,000hr⁻¹, preferably 300 to 6,000 hr⁻¹, more preferably 300 to 2,000 hr⁻¹;the average contact time with the catalyst can be from 0.01 to 10seconds or more, but is usually in the range of from 0.1 to 10 seconds,preferably from 0.2 to 6 seconds; the pressure in the reaction zoneusually ranges from 0 to 75 psig, but is preferably no more than 50psig. In a single pass mode process, it is preferred that the oxygen besupplied from an oxygen-containing gas such as air. The single pass modeprocess may also be practiced with oxygen addition. In the practice ofthe recycle mode process, oxygen gas by itself is the preferred sourceso as to avoid the build up of inert gases in the reaction zone.

Of course, in the oxidation reaction of the present invention, it isimportant that the hydrocarbon and oxygen concentrations in the feedgases be maintained at the appropriate levels to minimize or avoidentering a flammable regime within the reaction zone or especially atthe outlet of the reactor zone. Generally, it is preferred that theoutlet oxygen levels be low to both minimize after-burning and,particularly, in the recycle mode of operation, to minimize the amountof oxygen in the recycled gaseous effluent stream. In addition,operation of the reaction at a low temperature (below 450° C.) isextremely attractive because after-burning becomes less of a problemwhich enables the attainment of higher selectivity to the desiredproducts. The catalyst of the present invention operates moreefficiently at the lower temperature range set forth above,significantly reducing the formation of acetic acid and carbon oxides,and increasing selectivity to acrylic acid. As a diluting gas to adjustthe space velocity and the oxygen partial pressure, an inert gas such asnitrogen, argon or helium may be employed.

When the oxidation reaction of propane, and especially the oxidationreaction of propane and propene, is conducted by the method of thepresent invention, carbon monoxide, carbon dioxide, acetic acid, etc.may be produced as by-products, in addition to acrylic acid. Further, inthe method of the present invention, an unsaturated aldehyde maysometimes be formed depending upon the reaction conditions. For example,when propane is present in the starting material mixture, acrolein maybe formed; and when isobutane is present in the starting materialmixture, methacrolein may be formed. in such a case, such an unsaturatedaldehyde can be converted to the desired unsaturated carboxylic acid bysubjecting it again to the vapor phase catalytic oxidation with thepromoted mixed metal oxide-containing catalyst of the present inventionor by subjecting it to a vapor phase catalytic oxidation reaction with aconventional oxidation reaction catalyst for an unsaturated aldehyde.

Turning now in more specific detail to the third aspect of the presentinvention, the method of the present invention comprises subjecting analkane, or a mixture of an alkane and an alkene, to a vapor phasecatalytic oxidation reaction with ammonia in the presence of a catalystcontaining the above mixed metal oxide, to produce an unsaturatednitrile.

In the production of such an unsaturated nitrile, as the startingmaterial alkane, it is preferred to employ a C₃₋₈ alkane such aspropane, butane, isobutane, pentane, hexane and heptane. However, inview of the industrial application of nitrites to be produced, it ispreferred to employ a lower alkane having 3 or 4 carbon atoms,particularly propane and isobutane.

Similarly, as the starting material mixture of alkane and alkene, it ispreferred to employ a mixture of C₃₋₈ alkane and C₃₋₈ alkene such aspropane and propene, butane and butene, isobutane and isobutene, pentaneand pentene, hexane and hexene, and heptane and heptene. However, inview of the industrial application of nitrites to be produced, it ismore preferred to employ a mixture of a lower alkane having 3 or 4carbon atoms and a lower alkene having 3 or 4 carbon atoms, particularlypropane and propene or isobutane and isobutene. Preferably, in themixture of alkane and alkene, the alkene is present in an amount of atleast 0.5% by weight, more preferably at least 1.0% by weight to 95% byweight, most preferably 3% by weight to 90% by weight.

The purity of the starting material alkane is not particularly limited,and an alkane containing a lower alkane such as methane or ethane, airor carbon dioxide, as impurities, may be used without any particularproblem. Further, the starting material alkane may be a mixture ofvarious alkanes. Similarly, the purity of the starting material mixtureof alkane and alkene is not particularly limited, and a mixture ofalkane and alkene containing a lower alkene such as ethene, a loweralkane such as methane or ethane, air or carbon dioxide, as impurities,may be used without any particular problem. Further, the startingmaterial mixture of alkane and alkene may be a mixture of variousalkanes and alkenes.

There is no limitation on the source of the alkene. It may be purchased,per se, or in admixture with an alkane and/or other impurities.Alternatively, it can be obtained as a by-product of alkane oxidation.Similarly, there is no limitation on the source of the alkane. It may bepurchased, per se, or in admixture with an alkene and/or otherimpurities. Moreover, the alkane, regardless of source, and the alkene,regardless of source, may be blended as desired.

The detailed mechanism of the ammoxidation reaction of this aspect ofthe present invention is not clearly understood. However, the oxidationreaction is conducted by the oxygen atoms present in the above promotedmixed metal oxide or by the molecular oxygen in the feed gas. Whenmolecular oxygen is incorporated in the feed gas, the oxygen may be pureoxygen gas. However, since high purity is not required, it is usuallyeconomical to use an oxygen-containing gas such as air.

As the feed gas, it is possible to use a gas mixture comprising analkane, or a mixture of an alkane and an alkene, ammonia and anoxygen-containing gas, However, a gas mixture comprising an alkane or amixture of an alkane and an alkene and ammonia, and an oxygen-containinggas may be supplied alternately.

When the gas phase catalytic reaction is conducted using an alkane, or amixture of an alkane and an alkene, and ammonia substantially free frommolecular oxygen, as the feed gas, it is advisable to employ a methodwherein a part of the catalyst is periodically withdrawn and sent to anoxidation regenerator for regeneration, and the regenerated catalyst isreturned to the reaction zone. As a method for regenerating thecatalyst, a method may be mentioned wherein an oxidizing gas such asoxygen, air or nitrogen monoxide is permitted to flow through thecatalyst in the regenerator usually at a temperature of from 300° C. to600° C.

The third aspect of the present invention will be described in furtherdetail with respect to a case where propane is used as the startingmaterial alkane and air is used as the oxygen source. The proportion ofair to be supplied for the reaction is important with respect to theselectivity for the resulting acrylonitrile. Namely, high selectivityfor acrylonitrile is obtained when air is supplied within a range of atmost 25 moles, particularly 1 to 15 moles, per mole of the propane. Theproportion of ammonia to be supplied for the reaction is preferablywithin a range of from 0.2 to 5 moles, particularly from 0.5 to 3 moles,per mole of propane. This reaction may usually be conducted underatmospheric pressure, but may be conducted under a slightly increasedpressure or a slightly reduced pressure. With respect to other alkanessuch as isobutane, or to mixtures of alkanes and alkenes such as propaneand propene, the composition of the feed gas may be selected inaccordance with the conditions for propane.

The process of the third aspect of the present invention may beconducted at a temperature of, for example, from 250° C. to 480° C. Morepreferably, the temperature is from 300° C. to 400° C. The gas spacevelocity, SV, in the gas phase reaction is usually within the range offrom 100 to 10,000 hr⁻¹, preferably from 300 to 6,000 hr⁻¹, morepreferably from 300 to 2,000 hr⁻¹. As a diluent gas, for adjusting thespace velocity and the oxygen partial pressure, an inert gas such asnitrogen, argon or helium can be employed. When ammoxidation of propaneis conducted by the method of the present invention, in addition toacrylonitrile, carbon monoxide, carbon dioxide, acetonitrile,hydrocyanic acid and acrolein may form as by-products.

Turning now in more specific detail to the fourth aspect of the presentinvention, the treated catalyst exhibits peaks at diffraction angles(2θ) of 22.1°, 27.1°, 28.2°, 36.2°, 45.2°, and 50.0°. As compared withan untreated catalyst composition, the treated catalyst composition ofthe present invention exhibits an X-ray diffraction pattern having arelative increase in a diffraction peak at a diffraction angle (2θ) of27.1 degrees when compared with an untreated catalyst, which may exhibitno peak at all at 27.1 degrees.

The relative difference between peak intensities of treated versusuntreated compositions may be greater than 5%, more preferably greaterthan 10%, and still more preferably greater than 20% of the intensity ofthe untreated catalyst composition at the diffraction angle (2θ) of 27.1degrees. Without intending to be bound by theory, it is believed that atleast two phases (A and B) are present in the resulting mixed metaloxide catalyst and the treatment of the catalyst precursor with a sourceof NO_(x) results in an increase in phase B relative to phase A in theresulting catalyst. The increase in phase B is believed to contribute toimproved performance of the catalyst in terms of selectivity, reactivityand yield.

EXAMPLES

Catalyst Preparation

Example 1

100 mL of an aqueous solution containing ammonium heptamolybdatetetrahydrate (1.0 M Mo), ammonium metavanadate (0.3 M V) and telluricacid (0.23 M Te), formed by dissolving the corresponding salts in waterat 70° C., was added to a 1000 mL rotavap flask. Then 50 mL of anaqueous solution of niobium oxalate (0.25M Nb) and oxalic acid (0.31M)were added thereto. After removing the water via a rotary evaporatorwith a warm water bath at 50° C. and 28 mm/Hg, the solid materials werefurther dried in a vacuum oven at 25° C. overnight and then calcined.Calcination was effected by placing the solid materials in an airatmosphere and then heating them to 275° C. at 10° C./min and holdingthem under the air atmosphere at 275° C. for one hour; the atmospherewas then changed to argon and the material was heated from 275° C. to600° C. at 2° C./min and the material was held under the argonatmosphere at 600° C. for two hours. The final catalyst had a nominalcomposition of Mo₁V_(0.3)Te_(0.23)Nb_(0.125)O_(f). The catalyst, thusobtained, was pressed in a mold and then broken and sieved to 10-20 meshgranules for reactor evaluation.

Example 2

100 mL of an aqueous solution containing ammonium heptamolybdatetetrahydrate (1.0 M Mo), ammonium metavanadate (0.3 M V) and telluricacid (0.23 M Te), formed by dissolving the corresponding salts in waterat 70° C., was added to a 1000 mL rotavap flask. Then 10 mL of 5%aqueous HNO₃ and 50 mL of an aqueous solution of niobium oxalate (0.25 MNb) and oxalic acid (0.31 M) were added thereto. After removing thewater via a rotary evaporator with a warm water bath at 50° C. and 28mm/Hg, the solid materials were further dried in a vacuum oven at 25° C.overnight and then calcined. Calcination was effected by placing thesolid materials in an air atmosphere and then heating them to 275° C. at10° C./min and holding them under the air atmosphere at 275° C. for onehour; the atmosphere was then changed to argon and the material washeated from 275° C. to 600° C. at 2° C./min and the material was heldunder the argon atmosphere at 600° C. for two hours. The final catalysthad a nominal composition of Mo₁V_(0.3)Te_(0.23)Nb_(0.125)O_(f). Thecatalyst, thus obtained, was pressed in a mold and then broken andsieved to 10-20 mesh granules for reactor evaluation.

Example 3

100 mL of an aqueous solution containing ammonium heptamolybdatetetrahydrate (1.0 M Mo), ammonium metavanadate (0.3 M V) and telluricacid (0.23 M Te), formed by dissolving the corresponding salts in waterat 70° C., was added to a 1000 mL rotavap flask. Then 20 mL of 5%aqueous HNO₃ and 50 mL of an aqueous solution of niobium oxalate (0.25 MNb) and oxalic acid (0.31 M) were added thereto. After removing thewater via a rotary evaporator with a warm water bath at 50° C. and 28mm/Hg, the solid materials were further dried in a vacuum oven at 25° C.overnight and then calcined. Calcination was effected by placing thesolid materials in an air atmosphere and then heating them to 275° C. at10° C./min and holding them under the air atmosphere at 275° C. for onehour; the atmosphere was then changed to argon and the material washeated from 275° C. to 600° C. at 2° C./min and the material was heldunder the argon atmosphere at 600° C. for two hours. The final catalysthad a nominal composition of Mo₁V_(0.3)Te_(0.23)Nb_(0.125)O_(f). Thecatalyst, thus obtained, was pressed in a mold and then broken andsieved to 10-20 mesh granules for reactor evaluation.

Example 4

100 mL of an aqueous solution containing ammonium heptamolybdatetetrahydrate (1.0 M Mo), ammonium metavanadate (0.3 M V) and telluricacid (0.23 M Te), formed by dissolving the corresponding salts in waterat 70° C., was added to a 1000 mL rotavap flask. Then 30 mL of 5%aqueous HNO₃ and 50 mL of an aqueous solution of niobium oxalate (0.25 MNb) and oxalic acid (0.31 M) were added thereto. After removing thewater via a rotary evaporator with a warm water bath at 50° C. and 28mm/Hg, the solid materials were further dried in a vacuum oven at 25° C.overnight and then calcined. Calcination was effected by placing thesolid materials in an air atmosphere and then heating them to 275° C. at10° C./min and holding them under the air atmosphere at 275° C. for onehour; the atmosphere was then changed to argon and the material washeated from 275° C. to 600° C. at 2° C./min and the material was heldunder the argon atmosphere at 600° C. for two hours. The final catalysthad a nominal composition of Mo₁V_(0.3)Te_(0.23)Nb_(0.125)O_(f). Thecatalyst, thus obtained, was pressed in a mold and then broken andsieved to 10-20 mesh granules for reactor evaluation.

Example 5

100 mL of an aqueous solution containing ammonium heptamolybdatetetrahydrate (1.0 M Mo), ammonium metavanadate (0.3 M V) and telluricacid (0.23 M Te), formed by dissolving the corresponding salts in waterat 70° C., was added to a 1000 mL rotavap flask. Then 40 mL of 5%aqueous HNO₃ and 50 mL of an aqueous solution of niobium oxalate (0.25 MNb) and oxalic acid (0.31 M) were added thereto. After removing thewater via a rotary evaporator with a warm water bath at 50° C. and 28mm/Hg, the solid materials were further dried in a vacuum oven at 25° C.overnight and then calcined. Calcination was effected by placing thesolid materials in an air atmosphere and then heating them to 275° C. at10° C./min and holding them under the air atmosphere at 275° C. for onehour; the atmosphere was then changed to argon and the material washeated from 275° C. to 600° C. at 2° C./min and the material was heldunder the argon atmosphere at 600° C. for two hours. The final catalysthad a nominal composition of Mo₁V_(0.3)Te_(0.23)Nb_(0.125)O_(f). Thecatalyst, thus obtained, was pressed in a mold and then broken andsieved to 10-20 mesh granules for reactor evaluation.

Example 6

100 mL of an aqueous solution containing ammonium heptamolybdatetetrahydrate (1.0 M Mo), ammonium metavanadate (0.3 M V) and telluricacid (0.23 M Te), formed by dissolving the corresponding salts in waterat 70° C., was added to a 1000 ml rotavap flask. Then 50 mL of 5%aqueous HNO₃ and 50 mL of an aqueous solution of niobium oxalate (0.25 MNb) and oxalic acid (0.31 M) were added thereto. After removing thewater via a rotary evaporator with a warm water bath at 50° C. and 28mm/Hg, the solid materials were further dried in a vacuum oven at 25° C.overnight and then calcined. Calcination was effected by placing thesolid materials in an air atmosphere and then heating them to 275° C. at10° C./min and holding them under the air atmosphere at 275° C. for onehour; the atmosphere was then changed to argon and the material washeated from 275° C. to 600° C. at 2° C./min and the material was heldunder the argon atmosphere at 600° C. for two hours). The final catalysthad a nominal composition of Mo₁V_(0.3)Te_(0.23)Nb_(0.125)O_(f). Thecatalyst, thus obtained, was pressed in a mold and then broken andsieved to 10-20 mesh granules for reactor evaluation.

Evaluation and Results

Catalysts were evaluated in a 10 cm long Pyrex tube reactor (internaldiameter: 3.9 mm). The catalyst bed (4 cm long) was positioned withglass wool at approximately mid-length in the reactor and was heatedwith an electric furnace. Mass flow controllers and meters regulated thegas flow rate. The oxidation was conducted using a feed gas stream ofpropane, steam and air, with a feed ratio of propane:steam:air of1:3:96. The reactor effluent was analyzed by an FTIR. The results at a 3second residence time are shown in Table 1.

TABLE 1 Example Temp. C. % C3 Conv. % AA yield 1 390 41 17 2 350 63 34 3381 46 34 4 373 55 40 5 389 56 43 6 373 48 37

As gleaned from the above, the present catalyst compositions, whentreated according to the present invention performs better thanuntreated compositions of like empirical formula. The treated catalystcomposition exhibits at least 1.5, and more preferably 2, times theyield of reaction product as compared with an untreated catalystcomposition of like empirical formula.

A relative improvement in the conversion of the gaseous reactant (e.g.,alkane or alkene) of at least 10%, and more preferably at least 20% isobserved using the treated composition of the present invention, ascompared with an untreated composition under like processing conditions.

Comparative Examples A, B, C & D

(Mixed Metal Oxide Catalysts without NOx Treatment)

A catalyst of nominal composition Mo_(1.0)V_(0.3)Te_(0.23)Nb_(0.17)O_(x)was prepared in the following manner: 200 mL of an aqueous solutioncontaining ammonium heptamolybdate tetrahydrate (1.0M Mo), ammoniummetavanadate (0.3M V) and telluric acid (0.23M Te) formed by dissolvingthe corresponding salts in water at 70° C., was added to a 2000 mLrotavap flask. Then 200 mL of an aqueous solution of ammonium niobiumoxalate (0.17M Nb) and oxalic acide (0.155M) were added thereto. Afterremoving the water via a rotary evaporator with a warm water bath at 50°C. and 28 mm Hg, the solid materials were further dried in a vacuum ovenat 25° C. overnight and then calcined.

Calcination was effected by placing the solid materials in an airatmosphere and then heating them to 275° C. at 10° C./min and holdingthem under the air atmosphere at 275° C. for one hour; the atmospherewas then changed to argon and the material was heated from 275° C. to600° C. at 2° C./min and the material was held under the argonatmosphere at 600° C. for two hours.

The catalyst, thus obtained, was pressed and sieved to 14-20 meshgranules for reactor evaluation. 4 g of these granules were packed intoa stainless steel tubular reactor (inside diameter: 1.1 cm) for the gasphase oxidation of propane. The reactor was heated with an electricfurnace and fed with a mixture of propane, air and steam having a feedcomposition of 7% propane, 71% Air and 22% steam. The effluent of thereactor was condensed to a separate a liquid phase and a gas phase. Thegas phase was analyzed by gas chromatography, in an SRI 8610C gaschromatograph, equipped with MS and Porapak Q columns and TCD detectorand available from SRI Instruments, to determine the propane conversion.The liquid phase was also analyzed by gas chromatography, in an HP 6890gas chromatograph equipped with FFAP capillary column and an FIDdetector and available from Hewlitt-Packard, for the yield of acrylicacid.

The results along with residence time and reactor temperature are shownin Table 2 and FIG. 1.

TABLE 2 Residence Temperature Propane Acrylic Acid Acrylic Acid ExamplesTime (sec) (° C.) Conversion (%) Selectivity (%) Yield (%) Comp. Ex. A 3380 38 66 25 Comp. Ex. B 3 389 51 65 33 Comp. Ex. C 3 397 62 58 36 Comp.Ex. D 3 399 65 52 34

Comparative Examples E, F, G & H

(Mixed Metal Oxide Catalysts with NOx Treatment)

A catalyst of nominal composition Mo_(1.0)V_(0.3)Te_(0.23)Nb_(0.17)O_(x)was prepared in the presence of nitric acid in the following manner: 200mL of an aqueous solution containing ammonium heptamolybdatetetrahydrate (1.0M Mo), ammonium metavanadate (0.3M V) and telluric acid(0.23M Te) formed by dissolving the corresponding salts in water at 70°C., was added to a 2000 mL rotavap flask. Then 200 mL of an aqueoussolution of ammonium niobium oxalate (0.17M Nb), oxalic acid (0.155M)and nitric acid (0.24M) were added thereto. After removing the water viaa rotary evaporator with a warm water bath at 50° C. and 28 mm Hg, thesolid materials were further dried in a vacuum oven at 25° C. overnightand then calcined. Calcination was effected by placing the solidmaterials in an air atmosphere and then heating them to 275° C. at 10°C./min and holding them under the air atmosphere at 275° C. for onehour; the atmosphere was then changed to argon and the material washeated from 275° C. to 600° C. at 2° C./min and the material was heldunder the argon atmosphere at 600° C. for two hours.

The catalyst, thus obtained, was pressed and sieved to 14-20 meshgranules for reactor evaluation. 4 g of these granules were packed intoa stainless steel tubular reactor (inside diameter: 1.1 cm) for the gasphase oxidation of propane. The reactor was heated with an electricfurnace and fed with a mixture of propane, air and steam having a feedcomposition of 7% propane, 71% Air and 22% steam. The effluent of thereactor was condensed to a separate a liquid phase and a gas phase. Thegas phase was analyzed by gas chromatography, in an SRI 8610C gaschromatograph, equipped with MS and Porapak Q columns and TCD detectorand available from SRI Instruments, to determine the propane conversion.The liquid phase was also analyzed by gas chromatography, in an HP 6890gas chromatograph equipped with FFAP capillary column and an FIDdetector and available from Hewlitt-Packard, for the yield of acrylicacid.

The results along with residence time and reactor temperature are shownin Table 3 and FIG. 1.

TABLE 3 Residence Temperature Propane Acrylic Acid Acrylic Acid ExamplesTime (sec) (° C.) Conversion (%) Selectivity (%) Yield (%) Comp. Ex. E 3350 48 73 35 Comp. Ex. F 3 358 54 72 39 Comp. Ex. G 3 366 62 68 42 Comp.Ex. H 3 373 70 67 47

Comparative Examples I, J, K & L

(Pd Promoted Mixed Metal Oxide Catalysts without NOx Treatment)

A catalyst of nominal compositionMo_(1.0)V_(0.3)Te_(0.23)Nb_(0.17)Pd_(0.01)O_(x) was prepared in thefollowing manner: 200 mL of an aqueous solution containing ammoniumheptamolybdate tetrahydrate (1.0M Mo), ammonium metavanadate (0.3M V)and telluric acid (0.23M Te) formed by dissolving the correspondingsalts in water at 70° C., was added to a 2000 mL rotavap flask. Then 200mL of an aqueous solution of ammonium niobium oxalate (0.17M Nb), oxalicacid (0.155M) and palladium nitrate hydrate (0.01M Pd) were addedthereto. After removing the water via a rotary evaporator with a warmwater bath at 50° C. and 28 mm Hg, the solid materials were furtherdried in a vacuum oven at 25° C. overnight and then calcined.

Calcination was effected by placing the solid materials in an airatmosphere and then heating them to 275° C. at 10° C./min and holdingthem under the air atmosphere at 275° C. for one hour; the atmospherewas then changed to argon and the material was heated from 275° C. to600° C. at 2° C./min and the material was held under the argonatmosphere at 600° C. for two hours.) The catalyst, thus obtained, waspressed and sieved to 14-20 mesh granules for reactor evaluation. 4 g ofthese granules were packed into a stainless steel tubular reactor(inside diameter: 1.1 cm) for the gas phase oxidation of propane. Thereactor was heated with an electric furnace and fed with a mixture ofpropane, air and steam having a feed composition of 7% propane, 71% Airand 22% steam. The effluent of the reactor was condensed to a separate aliquid phase and a gas phase. The gas phase was analyzed by gaschromatography, in an SRI 8610C gas chromatograph, equipped with MS andPorapak Q columns and TCD detector and available from SRI Instruments,to determine the propane conversion. The liquid phase was also analyzedby gas chromatography, in an HP 6890 gas chromatograph equipped withFFAP capillary column and an FID detector and available fromHewlitt-Packard, for the yield of acrylic acid.

The results along with residence time and reactor temperature are shownin Table 4 and FIG. 1.

TABLE 4 Residence Temperature Propane Acrylic Acid Acrylic Acid ExamplesTime (sec) (° C.) Conversion (%) Selectivity (%) Yield (%) Comp. Ex. I 3342 35 77 27 Comp. Ex. J 3 356 44 75 33 Comp. Ex. K 3 372 58 69 40 Comp.Ex. L 3 382 66 64 42

Examples 7-10

(Pd Promoted Mixed Metal Oxide Catalysts with NOx Treatment)

A catalyst of nominal compositionMo_(1.0)V_(0.3)Te_(0.23)Nb_(0.17)Pd_(0.01)O_(x) was prepared in thepresence of nitric acid in the following manner: 200 mL of an aqueoussolution containing ammonium heptamolybdate tetrahydrate (1.0M Mo),ammonium metavanadate (0.3M V) and telluric acid (0.23M Te) formed bydissolving the corresponding salts in water at 70° C., was added to a2000 mL rotavap flask. Then 200 mL of an aqueous solution of ammoniumniobium oxalate (0.17M Nb), palladium nitrate hydrate (0.01M Pd), oxalicacid (0.155M) and nitric acid (0.24M) were added thereto. After removingthe water via a rotary evaporator with a warm water bath at 50° C. and28 mm Hg, the solid materials were further dried in a vacuum oven at 25°C. overnight and then calcined.

Calcination was effected by placing the solid materials in an airatmosphere and then heating them to 275° C. at 10° C./min and holdingthem under the air atmosphere at 275° C. for one hour; the atmospherewas then changed to argon and the material was heated from 275° C. to600° C. at 2° C./min and the material was held under the argonatmosphere at 600° C. for two hours. The catalyst, thus obtained, waspressed and sieved to 14-20 mesh granules for reactor evaluation. 4 g ofthese granules were packed into a stainless steel tubular reactor(inside diameter: 1.1 cm) for the gas phase oxidation of propane. Thereactor was heated with an electric furnace and fed with a mixture ofpropane, air and steam having a feed composition of 7% propane, 71% Airand 22% steam. The effluent of the reactor was condensed to a separate aliquid phase and a gas phase. The gas phase was analyzed by gaschromatography, in an SRI 8610C gas chromatograph, equipped with MS andPorapak Q columns and TCD detector and available from SRI Instruments,to determine the propane conversion. The liquid phase was also analyzedby gas chromatography, in an HP 6890 gas chromatograph equipped withFFAP capillary column and an FID detector and available fromHewlitt-Packard, for the yield of acrylic acid.

The results along with residence time and reactor temperature are shownin Table 5 and FIG. 1.

TABLE 5 Residence Temperature Propane Acrylic Acid Acrylic Acid ExamplesTime (sec) (° C.) Conversion (%) Selectivity (%) Yield (%) Ex. 7 3 35752 78 41 Ex. 8 3 361 60 76 46 Ex. 9 3 369 67 72 48 Ex. 10 3 377 72 71 51

Examples 11-14

(Pd Promoted Mixed Metal Oxide Catalysts with NOx Treatment and OxalicAcid Extraction)

A catalyst of nominal compositionMo_(1.0)V_(0.3)Te_(0.23)Nb_(0.17)Pd_(0.01)O_(x) was prepared in thepresence of nitric acid and extracted with oxalic acid in the followingmanner: 200 mL of an aqueous solution containing ammonium heptamolybdatetetrahydrate (1.0M Mo), ammonium metavanadate (0.3M V) and telluric acid(0.23M Te) formed by dissolving the corresponding salts in water at 70°C., was added to a 2000 mL rotavap flask. Then 200 mL of an aqueoussolution of ammonium niobium oxalate (0.17M Nb), palladium nitratehydrate (0.01M Pd), oxalic acid (0.155M) and nitric acid (0.24M) wereadded thereto. After removing the water via a rotary evaporator with awarm water bath at 50° C. and 28 mm Hg, the solid materials were furtherdried in a vacuum oven at 25° C. overnight and then calcined.

Calcination was effected by placing the solid materials in an airatmosphere and then heating them to 275° C. at 10° C./min and holdingthem under the air atmosphere at 275° C. for one hour; the atmospherewas then changed to argon and the material was heated from 275° C. to600° C. at 2° C./min and the material was held under the argonatmosphere at 600° C. for two hours. 30 g of the solid materials wereground and added to 100 mL solution of 30% oxalic acid in water. Theresulting suspension was stirred at 125° C. for 5 hrs in a Parr reactor,then the solids were collected by gravity filtration and dried in avacuum oven overnight at 25° C. The catalyst, thus obtained, was pressedand sieved to 14-20 mesh granules for reactor evaluation. 4 g of thesegranules were packed into a stainless steel tubular reactor (insidediameter: 1.1 cm) for the gas phase oxidation of propane. The reactorwas heated with an electric furnace and fed with a mixture of propane,air and steam having a feed composition of 7% propane, 71% Air and 22%steam. The effluent of the reactor was condensed to a separate a liquidphase and a gas phase. The gas phase was analyzed by gas chromatography,in an SRI 8610C gas chromatograph, equipped with MS and Porapak Qcolumns and TCD detector and available from SRI Instruments, todetermine the propane conversion. The liquid phase was also analyzed bygas chromatography, in an HP 6890 gas chromatograph equipped with FFAPcapillary column and an FID detector and available from Hewlitt-Packard,for the yield of acrylic acid.

The results along with residence time and reactor temperature are shownin Table 6 and FIG. 1.

TABLE 6 Residence Temperature Propane Acrylic Acid Acrylic Acid ExamplesTime (sec) (° C.) Conversion (%) Selectivity (%) Yield (%) Ex. 11 3 33358 78 45 Ex. 12 3 342 68 75 51 Ex. 13 3 347 74 74 55 Ex. 14 3 350 79 7156

As gleaned from Comparative Examples A-L and Examples 7-14, the presentpromoted catalyst compositions, when treated according to the presentinvention, i.e., with a source of NOx, performs better than untreatedcatalyst compositions of like empirical formula. In particular, it canbe seen from the data of Tables 2-6 and FIG. 1 that, at a given propaneconversion rate, the treated promoted catalyst compositions exhibit upto 10% greater AA selectivity as compared with untreated unpromoted andpromoted catalyst compositions of like empirical formula. Also, at agiven propane conversion rate, the data of tables 2-6 show that the AAyield of the treated promoted catalyst compositions is increased by atleast a few percent as compared with untreated unpromoted and promotedcatalyst compositions of like empirical formula.

All publications discussed in the foregoing are hereby expresslyincorporated by reference herein for all purposes. Catalysts disclosedtherein may also be treated using the techniques of the presentinvention.

1. A process for producing an unsaturated carboxylic acid, which comprises subjecting an alkane or a mixture of an alkane and an alkene to a vapor phase catalytic oxidation reaction in the presence of a catalyst containing a mixed metal oxide having the empirical formula J_(j)M_(m)N_(n)Y_(y)Z_(z)O_(o) wherein J is at least one element selected from the group consisting of Mo and W, M is at least one element selected from the group consisting of V and Ce, N is at least one element selected from the group consisting of Te, Sb and Se, Y is at least one element selected from the group consisting of Nb, Ta, Ti, Al, Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pt, Sb, Bi, B, In, As, Ge, Sn, Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Hf, Pb, P, Pm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu, and Z is selected from the group consisting of Ni, Pd, Cu, Ag and Au; and wherein, when j=1, m=0.01 to 1.0, n=0.01 to 1.0, y=0.01 to 1.0, z=0.001 to 0.1 and o is dependent on the oxidation state of the other elements, said catalyst composition having been formed from calcining an admixture including catalyst precursors and a source of NO_(x) for improving catalytic performance.
 2. The process according to claim 1, wherein said source of NO_(x) is selected from nitric acid, ammonium nitrate, ammonium nitrite, NO, NO₂ or a mixture thereof.
 3. The process according to claim 1, wherein said source of NO_(x) is nitric acid.
 4. A process for producing an unsaturated nitrile, which comprises subjecting an alkane, or a mixture of an alkane and an alkene, and ammonia to a vapor phase catalytic oxidation reaction in the presence of a catalyst containing a mixed metal oxide having the empirical formula J_(j)M_(m)N_(n)Y_(y)Z_(z)O_(o) wherein J is at least one element selected from the group consisting of Mo and W, M is at least one element selected from the group consisting of V and Ce, N is at least one element selected from the group consisting of Te, Sb and Se, Y is at least one element selected from the group consisting of Nb, Ta, Ti, Al, Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pt, Sb, Bi, B, In, As, Ge, Sn, Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Hf, Pb, P, Pm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu, and Z is selected from the group consisting of Ni, Pd, Cu, Ag and Au; and wherein, when j=1, m=0.01 to 1.0, n=0.01 to 1.0, y=0.01 to 1.0, z=0.001 to 0.1 and o is dependent on the oxidation state of the other elements, said catalyst composition having been formed from calcining an admixture including catalyst precursors and a source of NO_(x) for improving catalytic performance.
 5. The process according to claim 4, wherein said source of NO_(x) is selected from nitric acid, ammonium nitrate, ammonium nitrite, NO, NO₂ or a mixture thereof.
 6. The process according to claim 4, wherein said source of NO_(x) is nitric acid. 